U.S. Pat. No. 3,663,150 issued May 16, 1972 to William H. Hapgood discloses a system for controlling the fuel valve for a high capacity burner in which a sensor of material having a high positive temperature coefficient of electrical resistance is used to sense the presence of a flame following energization of a hot wire igniter and a fuel valve. Such a system performs satisfactorily when the time delay for closing the gas valve in the event of ignition failure is sufficiently long and/or the impedances of the fuel valve solenoid winding and time delay resistor are specially selected. However, where higher performance boilers require quicker response between the application of the fuel and the breaking of the circuit in the event of ignition failure or where standard solenoid windings and time delay relays are desired, current amplification of the flame sensor output is desirable.